1. Field of the Invention
The present invention is concerned with the extraction and recovery of zinc from zinc-bearing materials through a process carried out in a chloride-based media by chlorinating the metals followed by changing the media and performing electrowinning in a conventional sulfate electrolyte. This process also allows for the recovery of precious and other metals. The present invention further relates to a process for producing zinc oxide from a complex sulfide material, an apparatus for performing the process, and processes for recovering iron, copper, silver, and lead from a complex sulfide material. More particularly, the invention relates to a process of producing zinc oxide from such a complex sulfide material by, preferably, leaching the sulfide material with hydrochloric acid and oxygen, followed by precipitation of iron from the leach solution using magnesium oxide, and cementation of lead, copper, silver, cadmium and cobalt using zinc dust. Zinc oxide may then be precipitated from the leach solution using magnesium oxide. The residual magnesium chloride solution can then be spray roasted to regenerate hydrochloric acid and magnesium oxide.
2. Description of the Related Art
Use of chloride hydrometallurgy for the recovery of zinc from either complex sulfide ores or other metal-containing secondary materials offers many advantages over sulfate hydrometallurgical and pyrometallurgical processes. Concerns regarding the oversupplied market for sulfuric acid in North America and the shortage of conventional zinc concentrates have increased in recent years. De-coupling of zinc production from acid production and the processing of alternative feed materials offer a possible solution to these concerns. Gaining the ability to use a variety of zinc-bearing materials, such as difficult to process zinc concentrates or zinc containing wastes, has been the focus of numerous prior investigations. The recovery of precious metals from zinc concentrates and wastes, currently unachievable in most conventional electrolytic refineries, is another previously unrealized goal. The process of the present invention has been developed with these goals in mind.
This process aims to recover Zn, Ag, Cd, Cu and Pb from mineralogically complex sulfide concentrates and other zinc-bearing materials. Complex sulfide ores generally have a very high degree of mineral interlocking, and the minerals within them generally have small mineral grain size, making the production of saleable zinc and lead concentrates economically difficult or impossible using conventional mineral processing methods. Many deposits of these ores are known and could be exploited if adequate processing technology were available.
The HCl/O2 leach process of the present invention results in the extraction of valuable metals (e.g., Zn, Ag and Pb) from a low grade complex concentrate as produced from an ore body of complex sulphides. Metal concentrations of the typical concentrate used are: 17.0% Zn, 2.14% Pb, 0.21% Cu, 123 g/t Ag and 32.8% Fe, but the process is not limited to this composition. The process allows for the on-site treatment of low grade material, resulting in the production of an iron-free zinc oxide that can be shipped to an electrolytic zinc refinery, therefore cutting down on transportation and residue disposal costs. Alternatively, the zinc oxide produced could be sold directly to customers.
The chloride process of the present invention could be used on zinc ferrites (from zinc process residues), on EAF (Electric Arc Furnace) and BOF (Basic Oxygen Furnace) dusts, or any other zinc-bearing materials of this nature.
The ferric chloride leach developed by Canmet (Craigen, W. J. S., Kelly, F. J., Bell, D. H. and Wells, J. A., Canada Centre for Mineral and Energy Technology, Ottawa, ON, Canada, 26pp. 3 refs., (in English), June 1990) uses chlorine and ferric chloride to recover zinc from complex metal sulfides. A solution containing both zinc chloride and ferrous chloride is sent through a solvent extraction unit to remove iron and leave a clean zinc chloride solution, which is then sent to electrolysis to extract zinc and recover chlorine. However, this process is disadvantageous in that the cost of electrowinning zinc in chloride media is high.
U.S. Pat. Nos. 4,378,275 and 4,536,214 provide a process for recovering zinc from complex sulfides. Complex sulfide ores are leached in autoclaves in one or two stages, and cupric chloride is the agent responsible for leaching zinc sulfide. The leach solution is purified by zinc dust cementation, and iron is removed by precipitation with MgO. Zinc is recovered by solvent extraction (loading on DEHPA (di(ethylhexyl)phosphoric acid) and stripping by zinc sulfate electrolyte), followed by electrolysis. Recovery of reagents is accomplished by sending the resulting MgCl2 leach solution to a spray roaster where HCl and MgO are re-formed. This process involves multiple steps to produce a clean, organic-free electrolyte from a conventional zinc sulfate cellhouse. Furthermore, autoclaves are expensive pieces of equipment, unproven for use with chloride media involving oxidative solubilization.
U.S. Pat. No. 3,973,949 uses ferric chloride to leach zinc-containing materials. Zinc is purified by solvent extraction and then precipitated from the leach solution using sodium carbonate or sodium hydroxide. Reagents are recovered by electrolysis of sodium chloride solution in a chloro-alkali cell. Ferric chloride is regenerated using chlorine and oxygen. Two stages of solvent extraction are required. Thus, while environmentally acceptable and metallurgically elegant, this process is much more capital and operating cost intensive than the process of the present invention where MgCl2 is decomposed to regenerate MgO and HCl.
Additional processes have been used to extract metals from sulfide ores. In U.S. Pat. No. 4,026,773, a process for extracting metals, including zinc, from manganiferous ocean floor nodule ore is disclosed. The process comprises treating the ore with hydrochloric acid to produce a solution of the metal chlorides further process to manganese dioxide and selectively extract Fe, Cu, Ni, Co and Zn.
Similarly, in U.S. Pat. Nos. 4,206,023 and 4,346,062, zinc is recovered from materials containing zinc sulfide by partially chlorinating the zinc sulfide containing material in an aqueous medium.
U.S. Pat. No. 4,337,128 teaches a method of leaching sulfide-containing raw materials having metal sulfides of copper, iron, lead, silver, mercury and zinc. These raw materials are leached using a solution comprising cupric chloride and ferric chloride.
Copper and zinc are separated and recovered from aqueous chloride solutions containing lead, copper, zinc, and impurities in U.S. Pat. No. 4,362,607.
In U.S. Pat. Nos. 4,440,569, 4,443,253, 4,505,744, 4,510,028, 4,545,963, 4,832,925, and 5,380,354, zinc is recovered from zinc containing sulfidic materials that also contain iron and lead or silver by leaching the sulfidic material under oxidizing conditions.
U.S. Pat. No. 5,017,346 discloses a method of refining zinc oxide from roasted concentrates containing zinc sulfide by leaching the concentrates in an aqueous sulfur dioxide solution under controlled conditions, so as to provide selective separation of the zinc from the other elements contained in the concentrates.
Zinc may also be extracted from a sulfide ore or concentrate containing copper and zinc by subjecting the concentrate to pressure oxidation in the presence of oxygen and an acidic halide solution to obtain a pressure oxidation slurry, as shown in U.S. Pat. No. 5,869,012. This slurry is then subjected to a liquid/solid separation step to produce a liquor containing copper and zinc in solution.
Methods of purifying aqueous zinc solutions by using zinc dust to cement out impurities are also known. U.S. Pat. No. 4,637,832 discloses a method of cementing out impurities such as copper, cadmium, nickel, and cobalt from an aqueous solution of zinc sulfate by using zinc dust and an activator such as Cuxe2x80x94As or Cuxe2x80x94Sb.
It is desirable to develop a process for producing zinc oxide from complex concentrates of sulfide materials that is easy to perform and cost-effective. None of the above-mentioned techniques addresses a process of producing a clean zinc oxide that overcomes the problems noted above.
It is an object of the invention to provide an apparatus for producing zinc oxide from a complex sulfide material. The apparatus comprises a leaching unit for leaching the complex sulfide material with hydrochloric acid and oxygen, a first precipitating unit for precipitating iron from the leach solution using magnesium oxide, and removing, lead copper, silver, cadmium and cobalt from the leach solution by cementation with zinc dust. A second precipitating unit is used to precipitate zinc oxide from the leach solution using magnesium oxide. Then the residual magnesium chloride solution may be spray roasted to regenerate hydrochloric acid and magnesium oxide.
A further object of the present invention is to provide a process for producing zinc oxide from a complex sulfide material. The process comprises the steps of leaching the complex sulfide material with hydrochloric acid and oxygen, precipitating iron from the leach solution using magnesium oxide, cementing lead, copper, silver, cadmium and cobalt in the leach solution with zinc dust, and precipitating zinc oxide from the leach solution using magnesium oxide. The residual magnesium chloride solution may then be spray roasted to regenerate hydrochloric acid and magnesium oxide.
Still another object of the present invention is to provide a process for recovering copper, silver, and lead from a complex sulfide material. The process comprises the steps of leaching the complex sulfide material with hydrochloric acid and oxygen, precipitating iron from the leach solution using magnesium oxide, and recovering lead, copper, silver, cadmium and cobalt from the leach solution by cementing with zinc dust.
A further object of the present invention is to provide a zinc oxide precipitate that is substantially free of contaminants by leaching a complex sulfide material with hydrochloric acid and oxygen. Iron is precipitated from the leach solution using magnesium oxide, and copper, silver and lead are cemented from the leach solution using zinc dust. Zinc oxide is precipitated from the leach solution using magnesium oxide.